Solid-state synthetic support resins have been developed tremendously since the theoretical studies on the solid-state syntheses by R. B. Merrifield. Solid-state synthetic polymer support resins should have mechanically and chemically stable characteristics and allow easy introduction of functional groups and versatile linker bondages, as well.
Spherical polystyrene resin cross-linked with 1 or 2% divinylbenzene has attracted much attention in solid-state peptide syntheses due to stable mechanical characteristics and swelling properties in the solvent.
Other polymer supports for solid state syntheses with various properties have been reported. R. C. Sheppard et al. have reported on the preparation of polyamide resin, which has advantages in syntheses of acyl carrier protein fragment (65-74) over conventional polystyrene resin due to solvent affinity (J. Am Chem. Soc. Vol. 97, 6584-6585, 1975).
Introduction of hydrophilic polyethylene glycol to polystyrene resin yields TentaGel® resin with wide solvent affinities, and whereby it is especially useful for peptide syntheses as a hydrophilic support (E. Bayer, Angew. Chem. Int. Ed. Vol. 30, 113-119, 1991).
Modifying polystyrene with flexible cross-linking agent allows JandaJel™ resin, which gives better yield in syntheses of acyl carrier protein fragment (65-74) than polystyrene resin cross-linked with 1% divinylbenzene due to better swelling property (Tetrahedron Letters Vol. 43, 37-40, 2002).
Besides the above characteristics, distribution of the functional groups within the resin also affects characteristic of the supports for solid-state reaction, because it provides reactant with accessibility to the reaction site.
CutiCore® resin, prepared by copolymerization of styrene and macromer with polyethylene glycol structure, results in core-shell structure with the functional group presiding selectively on the surface.
CutiCore® resin has showed better yield in amino acid coupling reaction in the initial preparatory stage of solid-state peptide syntheses and photo-cleavage reaction from the resins, as compared with polystyrene resin or TentaGel® resin (Macromol. Chem. Phys. Vol. 203, 2211-2217, 2002).
Resins with the above core-shell structure can be prepared by different process. K. S. Lam et al. have reported on the derivatization of only outer layer of TentaGel® resin in two-phase solvents to render resins with core-shell structure (J. Am. Chem. Soc. Vol. 124, 7678-7680, 2002).
Resins with core-shell structure for photo reaction can be prepared from copolymerization of aminomethyl polystyrene and 2,4,6-trichloro-1,3,5-triazine, followed by grafting with diamino polyethylene glycol (Organic Letters Vol. 6 3273-3276, 2004).
Aminomethyl polystyrene resin can be widely applied in solid-state reaction, such as coupling reaction of liker and spacer, peptide syntheses, and various organic syntheses, as well.
One of the techniques for characterization of the resin is autoradiography; Merrifield et al. confirmed even distribution of reaction-sites inside of the aminomethyl polystyrene resin by autoradiography (J. Am. Chem. Soc. Vol. 102, 5463-5470, 1980).
Confocal microscope can be also used for the scrutinizing the reaction sites. S. R. McAlpine et al. examined an optical slice of ArgoPore resin (polystyrene grafted with polyethylene glycol) on a confocal microscope, and confirmed even distribution of the reaction site, in contrast with aminomethyl polystyrene resin.
However, M. Bradley and G. Yung argued that quenching or re-absorbing caused no fluorescence light emitting from the inside of an optical slice. This was verified by examining the cross-section of resin, and even distribution of the functional group of aminomethyl polystyrene resin was detected by confocal Raman spectroscopy, on the contrary to aforementioned McAlpine's report (Chem. Eur. J. Vol. 5, 3528-3532, 1999).
To introduce aminomethyl functional group on the benzene ring of polystyrene resin, the following preparatory procedures can be employed: chloromethylation-ammonia substitution, phthalimidomethylation-dephthaloylation, trifluoroamidomethylation-deacylation, and copolymerization of phthalimide monomer-dephthaloylation.
Random distribution of aminomethy group is usually achieved on the support resin by the above preparations. For example, trifluoroacetamidomethylation-deacylation is convenient preparation due to simple hydrolysis. However C—N in trifluoroacetylamide is weak enough to undergo a complete hydrolysis, even inside the resin. Therefore, the core-shell structure can't be obtained by employing this preparation. As a result, the reactions with the functional group take place mainly at the surface of the resin due to the limited accessibility of the inside functional group. Therefore, more efficient utilization of aminomethyl group can be achieved with selective dispersion of the functional group on the surface than the random distribution.
There has been a need in the art to overcoming the drawbacks of the prior arts. Therefore, development of economic and yet convenient preparation process for controlled dispersion of the aminomethyl group on the surface of polystyrene resin has attracted much interest for more efficient utilization of the functional group.